Self-propelled self-guiding lawn mower

Abstract

A fully automatic self-propelled self-guiding lawn mower in which guidance of the lawn mower is based on the principal of a magnet following a passive ribbon or wire of ferromagnetic material. The lawn mower includes two drive wheels located on opposite sides of the vehicle. Each drive wheel is connected to a drive shaft on the vehicle through a separate solenoid controlled clutch and each drive wheel is equipped with a separate electromagnet controlled brake. The drive shaft is turned at a constant rate of speed by a battery powered electric motor. The guidance system for controlling the movement and direction of the lawn mower includes a rotably mounted bar magnet horizontally aligned with the longitudinal axis of the vehicle and fixedly coupled to an electrical contact wiper arm that traverses an arcuate array of radially extending electrical contacts. Each one of the contacts is coupled to different ones or combinations of the actuators that operate the clutches and brakes and other mechanisms associated with the vehicle. The cutter assembly portion of the lawn mower includes two different sets of cutting blades, a first set for performing the majority of the cutting of the grass and a second set for trimming off ragged edges of grass that might be left by the first set of cutting blades. Cleaning vanes are also provided. The cutting blade tip speed is relatively very slow; being set at about 3500 feet per minute.

I claim: 
     
       1. An automatic self-propelled, self-steering lawn mower adapted to follow a passive ribbon or wire of ferromagnetic material or permanent magnet impregnated material comprising: (a) a prime mover, and   (b) a mower cutting attachment coupled to said prime mover,   (c) said prime mover comprising: (1) a frame,   (2) left and right drive wheels mounted on and at least partially supporting said frame,   (3) a motor driven drive shaft mounted on said frame,   (4) left and right solenoid operated clutch means for coupling the drive shaft to the left and right drive wheels respectively,   (5) left and right solenoids coupled to said left and right solenoid operated clutch means, respectively, and   (6) a guidance and control assembly rigidly mounted on the frame for sensing deviations in the path of travel of said prime mover relative to said passive ribbon or wire and in response to said deviations decoupling one or both of said clutch means so as to either cause said prime mover to turn in a direction so as to correct such deviations or cut off the power to said drive wheels and quidance and control assembly comprising:   (a) a housing, a shaft mounted on the housing for rotational movement about its longitudinal axis,   (b) a bar magnet fixedly mounted on the shaft for self-rotation toward said passive ribbon or wire about a substantially horizontal axis directed substantially fore-and-aft with respect to the prime mover, said magnet being eccentrically mounted on said housing so as to tilt to one side when not under the influence of said passive ribbon or wire,   (c) a rotary switch, said rotary switch having a freely movable rotor arm and a fixed stator, said stator having a plurality of contacts,   (d) said stator being fixedly mounted on the housing, said rotor arm being fixedly mounted on the shaft on the housing and said stator contacts being selectively connected electrically to said left and right clutch solenoids so as to selectively decouple one or both of said clutches according to the angular position of the magnet relative to the passive ribbon or wire.     
     
     
       2. The lawn mover of claim 1 and wherein said mower cutting attachment includes an aerodynamically clean dome, a rotatably mounted disk, a plurality of main cutting blades mounted on the periphery of said disk and a plurality of razor sharp auxiliary blades mounted on the periphery of said disk. 
     
     
       3. The lawn mower of claim 2 and wherein said main blades have a leading edge that tapers at about 14°, a trailing edge that tapers at about 6° and an angle of attack of about 14°. 
     
     
       4. The lawn mower of claim 3 and wherein said motor is battery driven and wherein said rotating disk is mechanically coupled to said motor and arranged to turn so as to provide a blade tip speed of about 3500 feet per minute. 
     
     
       5. An automatic self-propelled, self-steering lawn mower adapted to follow a passive ribbon or wire of ferromagnetic material or permanent magnet impregnated material comprising: (a) a prime mover, and   (b) a mower cutting attachment coupled to said prime mover,   (c) said prime mover comprising: (1) a frame,   (2) left and right drive wheels mounted on and at least partially supporting said frame,   (3) a motor driven drive shaft mounted on said frame,   (4) left and right solenoid operated clutch means for coupling the drive shaft to the left and right drive wheels respectively,   (5) left and right solenoids coupled to said left and right solenoid operated clutch means, respectively, and   (6) a guidance and control assembly for sensing deviations in the path of travel of said prime mover relative to said passive ribbon or wire and in response to said deviations decoupling one or both of said clutch means so as to either cause said prime mover to turn in a direction so as to correct such deviations or cut off the power to said drive wheels and guidance and control assembly comprising: (a) a magnet mounted for self-rotation toward said passive ribbon or wire about a substantially horizontal axis directed substantially fore-and-aft with respect to the prime mover,   (b) a rotary switch, said rotary switch having a freely movable rotor arm and a fixed stator, said stator having a plurality of contacts,   (c) said rotar arm being fixedly mounted relative to the magnet and said stator contacts being selectively connected electrically to said left and right clutch solenoids so as to selectively decouple one or both of said clutches according to the angular position of the magnet relative to the passive ribbon or wire,   (d) a housing, said magnet being eccentrically mounted on said housing so as to tilt to one side when not under the influence of said passive ribbon or wire, and   (e) a quantity of viscous fluid in the housing of said guidance and control assembly in contact with said manget for damping movement of said magnet.       
     
     
       6. The lawn mower of claim 5 and wherein said magent is a bar magnet having one of its poles facing downard and the other of its poles facing upward. 
     
     
       7. The lawn mower of claim 6 and wherein the prime mover further includes a separate brake mechanically coupled to each drive wheel, a separate electromagnet for energizing each brake and separate electrical means for connecting each electromagnet and solenoid to a particular contact on said stator. 
     
     
       8. The lawn mower of claim 7 and wherein the separate electrical means for connecting each stator contact to its respective solenoid or electromagnet includes electrical damping means for damping out sudden movements of the magnet caused by the prime mover travelling over rough or undulating terrain. 
     
     
       9. The lawn mower of claim 8 and wherein said stator contacts are arranged in an array extending radially outward from the axis of rotation of the magnet, said array comprising two groups of contacts symmetrically disposed about a central position, each group of contacts being electrically connected to the solenoid and electromagnet associated with one of the drive wheels. 
     
     
       10. A cutting attachment for use in a lawn mower comprising: a disk adapted to be mounted for rotation on said lawn mower, said disk having thereon a main set of cutting blades and an auxiliary set of cutting blades, the thickness of the auxiliary blades being razor thin and serving to trim ragged edges to grass left by the main set of cutting blades, the main set of cutting blades being thicker than the auxiliary set of blades and performing the basic cutting of the grass wherein said auxiliary set of blades each have a thickness of about between 20 and 30 thousandths of an inch and are thinner than said main set of blades.   
     
     
       11. The attachment of claim 10 and wherein said main set of blades have a thickness of about 1/4" at the center and a leading edge that tapers at an angle of about 14°. 
     
     
       12. The attachment of claim 11 and wherein said set of auxiliary blades are mounted on the periphery of the disk.